William Stallings Komunikasi Data dan Komputer

William Stallings Komunikasi Data dan Komputer Bab 2 Protokol dan Arsitektur

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Sistem Komunikasi Data

Karakteristik-karakteristik Langsung (direct) atau tidak langsung (indirect) Monolithik atau terstruktur Symmetric atau asymmetric Standard atau nonstandard

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Langsung (Direct) atau Tidak Langsung (Indirect) Direct Sistem-sistem membagi link point to point atau Sistem-sistem membagi sebuah link multi-point Data bisa lewat tanpa intervening active agent

Indirect Jaringan terswitch atau Internetwork atau internet Transfer data tergantung pada entitas yang lain

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Monolithik atau Terstruktur Komunikasi adalah sebuah tugas yang kompleks Dari kerumitan menjadi unit tunggal Rancangan terstruktur memecahkan masalah menjadi unit-unit yang lebih kecil. Struktur berlapis (Layered structure)

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Symmetric atau Asymmetric Symmetric Komunikasi antara peer entitas (peer entities)

Asymmetric Client/server

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Standar atau Nonstandar Protokol-protokol nonstandar dibangun untuk tugas-tugas dan komputer-komputer yang spesifik Sumber-sumber K dan penerima-penerima L mengarah kepada K*L protokol dan 2*K*L implementasi If common protocol used, K + L implementations needed

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Penggunaan Protokol Standar

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Fungsi-fungsi Encapsulation Segmentation and reassembly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services 12/27/2005


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Encapsulation Penambahan informasi kontrol ke data Informasi alamat Kode pendeteksian error Kontrol protokol

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Segmentation (Fragmentation) Blok-blok data dengan ukuran terbatas Pesan-pesan lapisan application mungkin saja berukuran besar Paket-paket network bisa jadi lebih kecil Membagi blok-blok besar menjadi lebih kecil disebut segmentation (atau fragmentation didalam TCP/IP) Blok-blok (sel-sel) ATM panjangnya 53 octets Blok-blok Ethernet (frames) mencapai panjang 1526 octets

Checkpoints and restart/recovery

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Mengapa memakai Fragment? Keuntungan Kontrol error yang lebih efisien Akses yang lebih adil ke fasilitas-fasilitas jaringan Delay-delay yang lebih pendek Dibutuhkan buffer yang lebih kecil

Kerugian Memiliki overhead-overhead Menaikkan intrupsi pada penerima (receiver) Waktu proses yang lebih banyak 12/27/2005


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Connection Control Membangun Koneksi Transfer data Terminasi Koneksi Memungkinkan connection interruption dan recovery Urutan angka digunakan untuk Pengiriman pesanan (Ordered delivery) Kontrol aliran (Flow control) Kontrol kesalahan (Error control)

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Transfer Data Berorientasikan Koneksi

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Ordered Delivery PDUs may traverse different paths through network PDUs may arrive out of order Sequentially number PDUs to allow for ordering

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Flow Control Done by receiving entity Limit amount or rate of data Stop and wait Credit systems Sliding window

Needed at application as well as network layers

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Error Control Guard against loss or damage Error detection Sender inserts error detecting bits Receiver checks these bits If OK, acknowledge If error, discard packet

Retransmission If no acknowledge in given time, re-transmit

Performed at various levels

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Addressing Addressing level Addressing scope Connection identifiers Addressing mode

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Addressing level Level in architecture at which entity is named Unique address for each end system (computer) and router Network level address IP or internet address (TCP/IP) Network service access point or NSAP (OSI)

Process within the system Port number (TCP/IP) Service access point or SAP (OSI)

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Address Concepts

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Addressing Scope Global nonambiguity Global address identifies unique system There is only one system with address X

Global applicability It is possible at any system (any address) to identify any other system (address) by the global address of the other system Address X identifies that system from anywhere on the network

e.g. MAC address on IEEE 802 networks 12/27/2005


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Connection Identifiers Connection oriented data transfer (virtual circuits) Allocate a connection name during the transfer phase Reduced overhead as connection identifiers are shorter than global addresses Routing may be fixed and identified by connection name Entities may want multiple connections - multiplexing State information

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Addressing Mode Usually an address refers to a single system Unicast address Sent to one machine or person

May address all entities within a domain Broadcast Sent to all machines or users

May address a subset of the entities in a domain Multicast Sent to some machines or a group of users

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Multiplexing Supporting multiple connections on one machine Mapping of multiple connections at one level to a single connection at another Carrying a number of connections on one fiber optic cable Aggregating or bonding ISDN lines to gain bandwidth

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Transmission Services Priority e.g. control messages

Quality of service Minimum acceptable throughput Maximum acceptable delay

Security Access restrictions

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OSI - The Model A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers 12/27/2005


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The OSI Environment

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OSI as Framework for Standardization

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Layer Specific Standards

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Elements of Standardization Protocol specification Operates between the same layer on two systems May involve different operating system Protocol specification must be precise ⌧Format of data units ⌧Semantics of all fields ⌧allowable sequence of PCUs

Service definition Functional description of what is provided

Addressing Referenced by SAPs 12/27/2005


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OSI Layers (1) Physical Physical interface between devices ⌧Mechanical ⌧Electrical ⌧Functional ⌧Procedural

Data Link Means of activating, maintaining and deactivating a reliable link Error detection and control Higher layers may assume error free transmission 12/27/2005


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OSI Layers (2) Network Transport of information Higher layers do not need to know about underlying technology Not needed on direct links

Transport Exchange of data between end systems Error free In sequence No losses No duplicates 12/27/2005Quality of serviceSistem Komunikasi Data

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OSI Layers (3) Session Control of dialogues between applications Dialogue discipline Grouping Recovery

Presentation Data formats and coding Data compression Encryption

Application Means for applications to access OSI environment 12/27/2005


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Use of a Relay

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TCP/IP Protocol Suite Dominant commercial protocol architecture Specified and extensively used before OSI Developed by research funded US Department of Defense Used by the Internet

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TCP/IP Protocol Architecture(1) Application Layer Communication between processes or applications

End to end or transport layer (TCP/UDP/…) End to end transfer of data May include reliability mechanism (TCP) Hides detail of underlying network

Internet Layer (IP) Routing of data

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TCP/IP Protocol Architecture(2) Network Layer Logical interface between end system and network

Physical Layer Transmission medium Signal rate and encoding

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PDUs in TCP/IP

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Some Protocols in TCP/IP Suite

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Required Reading Stallings chapter 2 Comer,D. Internetworking with TCP/IP volume I Comer,D. and Stevens,D. Internetworking with TCP/IP volume II and volume III, Prentice Hall Halsall, F> Data Communications, Computer Networks and Open Systems, Addison Wesley RFCs

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William Stallings Komunikasi Data dan Komputer

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